2006 BMW Z4 M Roadster

Sex-change operation is a success, kids.

We've been waiting for the M division of BMW to work its magic on the Z4 roadster since the two-seater debuted in '03. We spent 40,000 miles with a 2003 Z4 3.0-liter, and when we weren't exasperated by the dimwitted Sequential Manual Gearbox (SMG) and harsh ride, we imagined what the angular and chiseled droptop might be like with the M3's high-revving 333-hp inline-six. Apparently, the M guys were thinking the same thing but were too busy developing the V-10-powered 500-hp M5 and M6 to have time to perform what essentially turned out to be a sex-change operation on the Z4 roadster. We spent a day with the post-op Z4 M roadster in the south of Spain, and we can report that the surgery has been a success.

When the M5 debuted, we noted the M division had left many of BMW's latest innovations on the shop floor. Fine with us -- we didn't miss any of them. M cars are purged of run-flat tires, active steering, electric power steering, and active anti-roll bars. The Z4 M roadster does the other M cars one better by not even offering SMG. A traditional six-speed manual gearbox borrowed from the M3 is the only way the roadster will be sold. In the Z4, the gearbox benefits from shorter throws and a more direct feel. But it was the improved ride, which could likely be traced to conventional, non-run-flat tires, that we immediately noticed. Over the road the Z4 M roadster is more compliant and composed and less jarring than the base run-flat-equipped Z4 with 18-inch wheels. That and the absence of SMG had us already falling for the M roadster, and we hadn't even zinged the inline-six to its 7900-rpm power peak.

In the move to the Z4's engine bay, three horsepower were lost. However, 330 horses made the move as well as 262 pound-feet of torque. If you're thinking of slipping into something black to mourn the three-horse loss, this would be a good time to point out that the engine has roughly 200 fewer pounds to deal with here than it does in the M3 coupe. We expect the 330-hp roadster will accelerate from 0 to 60 in about 4.5 seconds, 0.3 second faster than the last M3 we tested and more than a half-second faster than a Porsche Boxster S.

After sitting all night in the cold, the Z4 M roadster takes a few minutes of driving for the mighty 3.2-liter to gradually awaken. As the engine oil warms, the adaptable redline that is present on all M-tweaked tachometers advances until it reaches 8000 rpm. Despite that high redline and elevated power peak (only 100 rpm shy of the redline), the 3.2-liter is flexible and willing to pull hard from just about any place on the dial and in any gear. A new exhaust system gives the Z4 M roadster a mellower and deeper voice than the M3's metallic and comparatively shrill tone. With the top down, the difference is immediately appreciated. With the top up, the engine sounds a bit grittier, louder -- and, yes, better -- than last year's 3.0-liter inline-six. The M guys must have scoffed at the idea of the silly subwoofer tube that connected the intake manifold to the fire wall to amplify the engine's sound; they have their own ways of making engines talk.

On the racetrack in Jerez, Spain, the M roadster showed itself to be a willing partner. There's more understeer in the chassis than in, say, a Honda S2000, but the M-tuned Z4 is at home on the track. Should you choose to switch off the stability control, the chassis will never surprise or commit any embarrassing faux pas. Huge cross-drilled rotors borrowed from the M3 Competition package measure 13.7 inches up front and 12.9 inches in back. Clamped by large single-piston calipers, the brakes slow the two-seater with alarming force and offer pedal feel that is good if not quite up to Porsche standards.

Acceleration out of a corner is drama-free, thanks to 255/40R-18 rear tires on nine-inch-wide wheels and the M3's beefy limited-slip differential that keeps you from spinning the inside rear tire. Another component shared with the M3 is the machine-shop- accurate hydraulic rack-and-pinion steering system that replaces the standard Z4's lighter-effort electrically assisted unit. Inside, a thick-rimmed leather-wrapped steering wheel does a good job of letting your hands know what the front tires are going through, but again, a Boxster's wheel manages to transmit more information, all of which you'll want to hear.

If you've ever sat in a Z4, the M version will be immediately familiar. In the M roadster, as in the Z4, you sit low and far back in the car behind a long hood and practically atop the rear wheels. This seating position gives the illusion of being in a larger vehicle than, say, a Boxster. In reality, the Boxster is nearly a foot longer than the BMW roadster. Special trim inside distinguishes the M from lesser Z4s. Leather that mimics the weave of carbon fiber graces the dash, and there's also the option of extended leather ($2700) that covers most of the interior in cowhide.

BMW set the $51,995 base price of the Z4 M roadster above that of the $49,595 M3, which will soon be going out of production, to be replaced next year by a 4.0-liter V-8 M3, but the roadster is less pricey than a $55,495 Boxster S. If you look at the specifications of both cars, the BMW with its spectacular engine wins out. However, aside from the BMW's engine, the Porsche still offers a more satisfying and sporting driving experience.

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